The present invention relates to an intersomatic implant for insertion in the discal space defined between two adjacent vertebrae in order to reestablish an appropriate height between the vertebrae and ensure that bone fusion takes place between said adjacent vertebrae.
The invention sets out more particularly to reestablish the discal space in the lumbar portion of the spinal column of a patient.
In the state of the art, it is known to insert an intersomatic implant in the discal space defined between two adjacent vertebrae. Numerous embodiments of such intersomatic implants have been proposed in the prior art. For example, patent FR 2 724 312 discloses a lumbar intersomatic implant in the form of a cage having two sagittal walls interconnected by an anterior transverse wall and a posterior transverse wall. Between them, the walls define an open volume for receiving spongy bone material for enhancing bone fusion between the two vertebrae. Such an implant presents an enlarged end portion giving it a kidney-shaped configuration making it possible to obtain a relatively large bearing area. Furthermore, the bottom and top edges of the walls of the cage are provided with spikes to retain the cage by anchoring in the bone of each adjacent vertebra. The design of such an implant is intended to avoid any migration of the implant either transversely or longitudinally once it has been inserted in a sagittal direction.
Although such an implant presents a large bearing area because of its kidney shape, it suffers from the drawback of sometimes requiring an approach path that is relatively large. It is also known, in particular from document EP 0 493 698 to provide a cage of generally rectangular shape offering the advantage of reducing the size of the approach path. Nevertheless, it is found that under certain conditions it is difficult to place the implant in the intervertebral space in a position enabling it to provide good stability between adjacent vertebrae, even though such stability is essential in order to obtain good bone fusion.
The Applicant has had the merit of designing a lumbar intersomatic implant adapted to provide the possibility of being placed in a position suitable for obtaining improved stability between two adjacent vertebrae by increasing the area of the support polygon, while nevertheless naturally also limiting the size of the approach path.
The object of the invention is thus to satisfy this need by proposing a lumbar intersomatic implant for insertion between two adjacent vertebrae via a limited approach path while nevertheless enabling it to be positioned in the vicinity of the side edges of the vertebrae in order to increase the area of the support polygon, and consequently to increase stability between said adjacent vertebrae.
To achieve such an object, the implant of the invention is a lumbar intersomatic implant for insertion into the discal space between two adjacent vertebrae for reestablishing the anatomical intervertebral space, the implant being in the form of a generally rectangular cage having two sagittal walls interconnected by at least an anterior transverse wall and a posterior transverse wall, the walls defining between them an open volume for filling with bone.
According to the invention, an xe2x80x9couterxe2x80x9d one of the sagittal walls of the implant presents:
a top rim and a bottom rim each shaped to present at least one retention edge extending substantially in the sagittal plane, making insertion via a posterior path possible; and
an outer face arranged to present a penetration-assisting shape enabling the cage to be offset transversely to a locking position in the discal space, which position is obtained by the retention edge preventing the cage from being reversed transversely.
In accordance with the invention, the intersomatic implant is inserted into the intervertebral space in a direction that is substantially parallel to the sagittal plane and it is thus designed to be capable of being moved transversely so as to come into the vicinity of the side edges of the vertebrae, thereby increasing the area of the support polygon between said two vertebrae.
A particularly advantageous application of the invention lies in being inserted via a single posterior unilateral path that is less damaging to the patient than the conventional broad approach path. It is possible to envisage inserting one or two lumbar intersomatic implants via a unilateral posterior path while nevertheless obtaining increased stability between said adjacent vertebrae. Installing such an implant via a unilateral posterior path makes it possible to avoid interrupting the structure of the spinous processes, to avoid forcing the paravertebral muscles hard and long, and to avoid inflicting circumferential fibrosis.